| Permafrost regions along the Qinghai-Tibet railway and Qinghai-Tibet highway, along the annual mean ground temperature in the range of 0 ?~4 ?, affected by negative temperature environment, the construction of the performance degradation of concrete structures, thus affecting the stability and security of structure. When the daily average outdoor temperature stability is lower than 5 ? for 5 days, concrete structure engineering winter construction measures should be taken, process trival cost is large, bring inconvenience to the construction and affect economic efficiency. With the rapid development of high performance concrete, the rational and effective use of mineral admixture is very important to improve the performance of concrete. The emergence of these problems requires us to have a systematic and deep research on the characteristics of low temperature condition and adding mineral admixtures cement hydration.In this paper, the physical and chemical properties and thermodynamic properties of the raw materials are analyzed. The key in the process of cement hydration, from the degree of hydration, the mesoscopic structure of cement stone and cement macroscopic mechanical properties of the three research perspective:1.The setting and hardening conditions of cement pastes with constant temperature in the chamber are simulated by artificial climate simulation test chamber, on this basis, the degree of cement hydration containing mineral admixture was measured quantitatively at low negative temperature curing environment;2. In the lab, make cement specimens of the same curing condition, mechanical properties were measured, it reflects the strength properties of macroscopic;3.Use of hardened concrete porosity analyzer, the cement specimens of processing mesoscopic pore structure analysis;4. In the course of the experiment, the relationship between the main factors affecting the hydration of cement was analyzed and compared;5. The cement gelled material characteristics and hydration mechanism of pure cement paste and cement paste with mineral admixture were analyzed qualitatively.After a lot of experiments and theoretical analysis, it is concluded that the degree of cement hydration adding mineral admixtures low negative temperature, mechanical properties and pore structure characteristics of the cement stone, at the same time, compared with the characteristics of cement hydration under standard curing condition, Analyses the similarities and differences between them. In addition, the relationship between the three were analyzed, in order to provide a theoretical basis for further study of the hydration process and hydration mechanism of the composite cementitious system. The results showed that: under the same age, affected by the low negative temperature drop in cement hydration, increase in large holes, small holes to reduce uneven distribution of pore structure, lower strength of cement stone; when adding mineral admixtures, the early stage of cement hydration was decreased, through the analysis of experimental data, mineral admixtures have refined the effect of pore structure; at the same time by using the experimental data fitting of the curve, put forward the best content of mineral admixture is satisfied with the requirement of strength and durability is 15% under the condition of low negative temperature.this paper introduces the analysis and the theoretical basis of hydration heat and the accessor methods of some main parameters and the determination methods of cement hydration heat.This study provides a theoretical basis for the reasonable application of concrete in low negative temperature environment, at the same time, to provide a new scientific basis for the effective utilization of mineral admixture, it has practical significance for the design and construction of concrete as well as the later maintenance, for the study of cement hydration for further expansion. |
PDF Full Text Request